Tuning scale



H. M. LEWIS 1,987,857

TUNING SCALE Filed Sept. 25, 1931 2 Sheets-Sheet 1 Hana:

INVENTOR HAROZD lV/ZZEl? (Eh A5 ATTORNEYS Jan. 15, 1935.

EEEAK H. M. LEWIS TUNING SCALE Jan. 15, 1935.

Filed Sept. 25, 1931 2 Sheets-Sheet 2 LIN/(A765 7-0 INVENTOR jw/TU/ HA R040 MILLER LfW/S I BY ATTORNEYS Patented Jan. 15, 1935 UNITED STATES TUNING SCALE Harold Miller Lewis, Douglaston, N. Y., assignor to Hazeltine Corporation Application September 25, 1931, Serial No. 565,027

15 Claims.

The present invention relates to a tuning system, or, more particularly, to such a system as adapted for use in a short wave receiver or converter.

A short wave converter is an apparatus which, when used in conjunction with any broadcast receiver, permits the reception of short wave signals by the said broadcast receiver. The converter comprises an oscillator and modulator, by which the short wave signal currents are converted into currents of a frequency within the tuning range of the broadcast receiver. The current of this frequency, which frequency will be referred to hereinafter as the intermediate frequency, is amplified, detected and reproduced by the broadcast receiver.

The frequency range covered by the short wave lillld is approximately from 1500 kc. (200 meters) to 20,000 kc. (15 meters). This range of frequencies is so great that it is not practical to tune a circuit through the entire range by the variation of a single tuning element. Some arrangement must be provided for changing both of the frequency determining elements; that is, both the inductance and the capacity. In accordance with the usual practice, the tuning is actually done by varying the capacity of a variable condenser, and the inductance is changed in steps to permit the condenser to tune the circuit throughout the various portions of the range.

In practicing the present invention, the. short wave band is dividedinto three bands which will be referred to in this application as the short wave band, the middle wave band, and the long wave band.

The inductance used in tuning the radio frequency circuits of the short wave receiver, or the radio frequency circuit and oscillator circuits of a converter, are usually wound on removable forms commonlyknown as plug-in coils, which coils are changed when desiring to go from one of the short wave bands to another. A system of this type has the disadvantages that it is expensive to manufacture and requires shifting of coils when operating.

Various systems have been proposed by which the inductance of the tuning coils is changed in steps by means of switches. However, the leads and switch mechanisms introduce capacities which considerably lessen the range of the tuning condensers, and usually the resulting large number of points to be switched has condemned this system.

However, in the usual receiver or converter in which the inductances are of the plug-in coil type, or in which switches are used to change the inductances, the tuning condenser has a single scale which is arbitrarily marked. This requires noting the coil in use or switch position, as well as the condenser setting, when logging a station,

as it is necessary to know both the scale indication and the inductance in order to tune the circuits to a given frequency.

It is the object of the present invention to overcome the above noted diflioulty and to proe vide an indicating'device for a short wave receiving apparatus in which the frequency to which the tuning device is tuned may be re.- corded, regardless of the band in which the set is being operated, and, further, to provide means by which the frequency band in which the set is being operated is indicated at all times.

Furthermore, the usual scale used in connection with the short wave receiver or converter permits operation of the apparatus with considerably more ease in the long wave band, due to the fact that the movement of the tuning control required toseparate the different stations at the long wave end of the band is considerably greater than that required to separate the stations at the short wave end of the band. It is, therefore, the further object of this invention to provide a scale in which thestations are separated by approximately the same amount at both ends of the tuning range.

These and further objects of my invention will become apparent from the following specifications taken in connection with the appended claims and with the accompanying drawings.

In accomplishing the objects of the present invention the inductances of the frequency determining circuit of the oscillator and the input circuit are provided with switches for short-circuiting the long wave and middle wave portions of the winding, when operating the oscillator, to receive signals in the middle wave band and short wave band, respectively. a

In order to permit continuous rotation of the tuning dial in either direction to progressively tune the converter through the entire band, the condensers used in both'the modulator input and oscillator circuits are each provided with double stators and double rotors so constructed that when the capacity between one of the pair oi. ro-

tors and stators is maximum, that between the other pair of rotors and stators is minimum. This feature is covered more particularly in application of William A. MacDonald for Condensers, Serial No. 564,997, filed concurrently herewith.

The tuning control knob is geared'to the condenser by 4:1 reduction gear. In turn the condenser is geared to the dial by a 2:1 step-up gear so that 180 rotation of the condenser corresponds to a full rotation of the dial. The dial rotates in the direction in which the tuning knob is turned. As the dial moves from left to right the frequencies received become higher. This dial has thereon three indicating scales, the outer scale being for indicating the frequencies in the short wave band, and the inner scale being for indicating the frequencies in the long wave band. The scales pass by indicator lights placed behind the dial within a compartment which permits illumination of but a single scale by each indicator light, and a switch operated simultaneously with the wave changing switches operates to light the appropriate scale. The long wave scale indications appear at the bottom window and the top window permits observation of the short wave scale indications. This arrangement allows a greater spread for the short wave channels of which there are considerably more than the long wave channels.

In order to permit the operation of a single control knob to control the frequency of reception, regardless of which of the three bands the converter is operating in, there is provided a gang switch mechanism operated by means of the condenser control knob at the appropriate instant as the dial is rotated from one to another of the frequency bands. The specific details of the switching arrangement constitute no part of the present invention, but are described fully in copending application of Harold Miller Lewis for Switching arrangement, Serial No. 565,026, filed concurrently herewith.

It can thus be seen that an arrangement has been provided by which the set can be tuned through the entire short wave band by the operation of a single control, and by which the frequency for which this apparatus is set to respond is automatically indicated at all times as the set is tuned.

Attention is now invited to the accompanying drawings in which:

Fig. 1 is a circuit diagram of a converter embodying the present invention; and

Fig. 2 and 3 are front and side elevations, respectively, of the indicator dial and control arrangement of the converter comprising a part of the present invention.

Fig. 3a is an inverted plan view of the switch control mechanism.

Referring now to Fig. 1. the antenna circuit includes the antenna 10, the ground 11, the trap circuit 12, comprising the inductance 13 and condenser 14, the primary winding 15, and a portion of the secondary winding 16. The inductance 13 and the condenser 14 of the trap circuit 12 are so proportioned that said circuit is resonant to the intermediate frequency produced by the short wave converter. The input circuit of the converter is connected to the grid of modulator device 1'7. which may be any thermionic tube, though that shown is of the screen grid type. The input circuit is tuned by means of the condenser 21, which may be a double condenser employing. as shown, a single rotor and two stators so arranged that the capacity obtained between the rotor and one stator is maximum, when the capacity between the rotor and the other stator is. minimum. The connections to the stators are controlled by means of the switch 23. The actual condenser includes two stators and two rotors, so arranged that when one rotor is entirely within its stator. the other rotor is entirely out of its stator. This is fully described in the application mentioned above. The function of the condenser and switch arrangement will be explained later.

The tapped secondary 16 is connected by means of switch 24, so that any of the tapped portions of the secondary may be included in the input circuit. The switch is so connected that the unused portions of the winding are short-circuited.

For producing the heterodyne frequency for combining with the incoming signal and thus producing the intermediate frequency, there is provided the oscillator 25. This oscillator tube is of the single grid type and includes in its grid circuit the secondary 40 of the oscillation transformer, the primary 42 of which is connected in the plate circuit which includes stopping condenser 43. The secondary 40 is a tapped winding similar to 16 of the antenna transformer, and the connections to said secondary are controlled by means of switch 34. The grid return of the oscillation circuit is completed through the biasing resistor 2'7, which is connected to the cathode of the tube 25. The frequency of the oscillation circuit is determined by means of condenser 31, which is similar to condenser 21. and is connected to be operated therewith in a uni-control manner by means of the control knob 22 associated with the indicator dial 26.

The connections to the two portions of the condenser 31 are controlled by means of switch 33.

Padding condensers 41M and 418 are provided across the two portions of condenser, as shown, for the purpose of aligning the oscillation circuit with the input of modulator 17 in the middle wave range and short wave range, respectively. Padding condenser 41L is connected across the long wave portion of the inductance winding 40, so that when the switch 34 is on contact L this condenser is practically in shunt with the condensers 31 and 41$ for adjusting the alignment in the long wave range. When the switch 34 is on contact M, the condenser 41L is in shunt with condensers 3'7 and 37', and the total series capacity is at that time the sum of these three condensers. I

In series with condenser 31 are provided series condensers 36, 3'7 and 38, the connections to which are controlled by means of the switch 35. Each of these condensers is provided with the padding condenser 36', 37', or 38', respectively, for the purpose of correcting the alignment of oscillator circuit with the modulator input in the various frequency bands. In the middle frequency band, as has just been stated, the condenser 41L is in shunt with 37 and 3'7. Coupling coils 44 and 45 coupled to the middle and long wave portions of the secondary 40, respectively, are included in the cathode circuit of the modulator 17. This circuit also includes the biasing resistor 46 shunted by by-pass condenser 4'7 for the purpose of causing tube 1'7 to act as a modulator.

The plate and screen grid potential are provided by means of the power supply source which, as shown, is of the ordinary double wave rectifier and filter type. This power supply also provides heater lighting current for heating the cathodes of tubes 1'7 and 25. A resistor 29 is included in the plate lead of the modulator for the purpose of reducing the plate potential thereof.

As shown, the dial 26 includes three scales, 26a, 26b, and 260, these scales covering the short wave band, middle wave band, and long wave band, respectively. I

It is to be noted that in order to get better spacing of the frequency indicators, the short wave scale is placed in the outer position on the dial 26, as the condenser motion to get the frequency separation required to separate the various stations is less in the short wave band than it is in the long wave band.

In furtherance of this general idea, the tuning condensers may be chosen to give a straight-line frequency characteristic, which gives an equal their radii, may be properly chosen so that all of the scales shall have the same uniform frequency spacing.

If the ratio of maximum to minimum frequency of the scales is 2 to 1, for example, the band of frequencies covered by each of the scales will bear the same ratio. In other words, if for example the long wave band width is 1600 kc., the middle wave band width will be 3200 kc., and the short wave band width willbe 6400 kc. This, then, will require a 2 to 1 ratio between the diameters or radii of the successive scales if the scale spacing is to be equal on all three scales. Then the radius of the middle wave scale will be twice that of the long wave scale, and the radius of the short wave scale will be twice that of the middle wave scale or four times that of the long wave scale.

The use of wider wave bands will separate the scales by a proportional amount.

For the purpose of indicating in which of the frequency ranges the converter is operating. each of the scales is provided with one of the illuminating lights 71d, 71!), or 71c, controlled by means of switch 39 to light them when tuning through the short wave band, middle wave band, and long wave band, respectively.

Switches 23, 24, 33, 34, 35 and 39 are so arranged as to be simultaneously operated and also to be actuated by the control knob 22 as the condensers are tuned through the limiting capacities for one of the frequency bands. Thus, the rotation of the control knob 22 results in the actuation of the switches 23 and 33, resulting in switching of the connections to condensers 21 and 31, respectively, to give the opposite capacity extreme for the modulator and oscillator circuits; Switch 39 is simultaneously operated changing the lighting of the indicating lights and thus indicating the change in the frequency band by changing the indication from one to another of the scales. Although specific means for actuating the switches constitute no part of the present invention, and are described fully in application, Serial No. 565,026, referred to above, they will be described briefly hereinafter.

Included in the plate supply to the modulator 17 is the inductance 50. This inductance may have a high, inherent capacity as indicated by capacity 51, or an actual condenser may be placed in shunt therewith. The inductance and capacity, however, are so proportioned that frequencies other than the desired intermediate frequency will be. by-passed.

A connection from the output of modulator 17 is made through condenser 52 and lead 53 to the antenna binding, post of the receiver 57. This connection is made through a shielded cable 54,

which may, for example, be a BX cable, from the.

walls of which the lead 53 is spaced by means of bakelite spacers 56. Also connected through the cable 54 is the ground connection 55, which is connected to the ground binding post of receiver 57. The capacity 52 and the inherent capacity between the leads 53 and 55 are so proportioned that they constitute a dummy antenna to'properly load the modulator 17, and to prevent misalignment of the input of receiver 57. Switch 59 is provided between the antenna 10 and the lead 53 by means of which the antenna may be directly connected to the input of the receiver 57 when it is desired to receive signals in the broadcast band directly on receiver 57.

The receiver 57 may be of any well known type, and is provided with the usual sound reproducing device 58. The specific details of neither 57 nor 58 constitute any part of the present invention.

The receiver is tuned to the intermediate frequency which it is desired to utilize, preferably 1,000 kc. The direct reception of signals of 1,000 kc., when the set is being operated to receive short wave signals by means of the converter, is prevented by means of the shielded cable 54. The modulator is prevented from acting as an amplifier of signals of 1,000 kc. frequency by meansof trap circuit 12. Any signals of a frequency other than 1,000 kc. in the output of modulator 17 would be excluded by the inductance 50. It is thus seen that a number of provisions have been made to prevent the interference of broadcast signals with the short wave signals being receive by means of the converter.

Attention is now invited to Figs. 2, 3 and 3a which show front and side elevations, and inverted plan view respectively, of the indicator dial and condenser and switch control mechanism. The chassis of the converter is represented at 100, and has the condenser 21 mounted thereon in a central position, a portion only of which is shown in Fig. 2. The shaft 93 of the condenser has a gear 102 and a switch throw-bar 104 secured on the end thereof, the function of which will be described more 'fully hereinafter.

The control knob 22 is mounted on shaft 116 and is journaled in the front of the chassis 100.

A gear 118, secured to said shaft, meshes with the gear 102. The gears 102 and 118 are so proportioned that a 1:4 ratio is provided. For per mittingthis engagement the chassis is provided with an opening or cutaway portion 119, which also permits the switch throw-bar 104 to pass therethrough and engage the switch shifting gear 122.

Also mounted on the chassis 100 are the vertical supporting member 108 and the front panel member 106. Mounted in the vertical member 108 is the journal 109, in which is journaled the shaft 110 to which is secured the indicator dial 26. Secured also to the shaft 110 is the gear 112 which meshes with the gear 102 on the condenser shaft 93.

Mounted upon the vertical member 108 is the hood member 114 providing three small compartments in which are mounted the indicator lights- 71a, 71b'and 71c. It can be seen that the dial 26 passes over the front of the compartments and the light passing therethrough is framed by the viewing window openings a, 120b, and 1200, respectively, cut in the panel member 106.

' A vertical wire 121 is arranged over the openings in the front of chambers 114 to provide an index mark which is visible only through that portion of the dial which is illuminated by, one of the lights 71.

The switch 124 is provided for controlling the power supply to the converter.

The gear 112 has half as many teeth as the gear 102, and the gear 118 has one-fourth as many. .Thus it can be seen that the scale 26 will rotate once for every half revolution of the condenser shaft 93, and for every two revolutions of the tuning control lmob.

The switch-throw bar 104 passes through an opening 119 in the chassis 100 and engages the teeth 142 of the switch-shifting gear 122 which latter is pivoted beneaththe chassis. The pin 141 on the gear 122 is connected by any appropriate linkage to control the motion of the switch arms of the gang switch. Each time the condenser rotor has made one half revolution, one end of the throw-bar engages a tooth 142 of the gear 122 and rotates it through a small angle. Thus the switch throw-bar 104 actuates a gang switch so that each time the condenser rotor has made one-half revolution, the switch, full details of which are shown in the copending application referred to above, will be actuated to change the connections to shift the frequency band in one direction or the other. The switch 39 which is included in the gang switch operates to light the appropriate indicator light, and thus the scale in which the apparatus is set to operate is indicated at all times.

Whereas, the above description of the features of the present invention refers particularly to a converter for converting the incoming short wave signal to a current of a frequency within thebroadcast band to which an ordinary receiver can tune, it is obvious that the features relating to a tuning system and indicating system as required in the short wave band are equally applicable to a short wave receiver of the ordinary type.

I claim: I

1. In a radio receiver adapted to receive radio signals covering a broad band of wave lengths, and including continuously variable reactances to tune through,various portions of the wave length band, thecombination of a chassis, reactance varying means mounted thereon, including a shaft, a panel mounted on said chassis, including viewing windows, a; supporting member also mounted on said chassis, control means mounted on said chassis, including a shaft having a knob and a gear mounted thereon, and a gear mounted on said reactance varying shaft adapted to mesh therewith, a multiple switch adapted to control the portion of the wave length band through which the receiver is adjusted to operate, an intermittent switch operating mechanism secured to said chassis and adapted to be operated by said reactance varying shaft when operated beyond the positions giving the limiting values of reactance, a dial shaft mounted on said supporting member, a dial mounted on said dial shaft, a gear mounted on said dial shaft and adapted to cooperate with the gear on said reactance varying shaft, three scales on said dial adapted to pass behind said viewing windows, an indicator wire across said windows adapted to indicate the scale position, a compartment behind each of said scales in line with said windows, an indicator light in each of said compartments, a connection between said indicator lights and said switch, whereby as said reactance varying means is varied past predetermined-limits, said switch will be operated to alter the connections to said indicator lights and thus change the scale indication lights to correspond with the change in the portion of the wave length band.

. 2. In a radio receiver adapted to receive radio signals covering a broad wave length band and employing reactance elements variable in steps to permit tuning" throughout various portions of the band, the combination with a variable reactance element for tuning throughout the various portions of the band, of an indicator dial associ-' ated with said element and operative therewith to indicate the position of said element, a plurality of scales on said dial each bearing indicia of the wave lengths covered by said variable reactance element while operating to tune within the respective portions of the wave length band, means for indicating the scale covering the portion of the hand through which the variable reactance is then adjusted to tune, a control means for operating said variable reactance element, and means operated by said control means when said variable reactance element is operated past its limits to simultaneously alter the reactances which are variable in steps, and change said indicator.

3, In a receiver adapted to receive signals covering a broad wave length band in which an inductance is varied in steps to permit tuning through various portions of the band, a variable condenser, an indicator dial operative with said variable condenser, a plurality of scales on said dial, said scales being spaced from the center of said dial by such a distance that they each have substantially the same frequency indication separation, an indicating means for indicating the position of said variable condenser, and means for changing the scale relative to which said indicating means is effective as the inductance of a circuit of the receiver is altered in steps.

4. In a radio receiver adapted to receive signals covering a broad wave length band, which receiver includes an inductance variable in steps to permit tuning through the various portions of said band, the combination of a variable tuning element, a dial associated with said element and movable therewith, a plurality of scales on said dial, each of said scales having such a radius that the frequency separation thereon will be substantially the same for the several scales, indicating means for indicating the position of said element on said dial, means for indicating which of the several scales represents the portion of the wave length hand through which the receiver is adjusted to tune, and means controlled by the motion of said tuning element past the positions giving the limiting reactance values of said element to simultaneously alter said last mentioned means and the portion of the wave length hand through which said receiver is adapted to tune.

5. In a radio receiver adapted to receive signals covering a broad wave length band, which receiver includes an inductance changeable in steps to permit tuning throughout various portions of said band, the combination of a variable tuning element, a dial associated with said element and movable therewith, a plurality of scales on said dial, each of said scales having such a radius that the frequency separation thereon will be substantially the same for the several scales, indicating means for indicating the position of said variable condenser, and means for designating the scale relative to which said indicating means is efl'ective as said inductance is changed. I 6. In a radio receiver adapted to receive radio signals covering a broad wave length band and employing reactance elements variable in steps to permit tuning throughout various portions of the band, the combination with a variable reactance element for tuning throughout the various portions of the band, of an indicator dial associated with said element and operative therewith to indicate the position of said element, a plurality of scales on said dial, each bearing indicia of the frequencies covered by the variable reactance element while operating to tune within the respective portions of the frequency band, means for indicating the wave length to which said receiver is tuned regardless of the portion of the band within which said receiver is being operated, a control means for operating said variable reactance element, and means operated by said control means when said variable reactance element is operated past its limits to simultaneously alter the reactances which are variable in steps, and select the scale relative to which said indicator is operative.

7. In a receiver adapted to receive signals covering a broad band of wave lengths, in which an inductance is varied in steps to permit tuning through various portions of the band, a variable condenser, an indicator dial operative with said variable condenser, a plurality of scales on said dial, said scales being spaced from the center of said dial by such a distance that they each have substantially the same frequency indication separation, an indicating means for indicating the frequency to which said receiver is tuned to respond, and means for designating the scale relative to which said indicating means is effective as the inductance of a circuit is altered in steps.

8. In a radio receiver adapted to receive signals covering a broad wave length band, which receiver includes an inductance variable in steps to permit tuning through the various portions of said band, the combination of a variable tuning element, a dial associated with said element and movable therewith, a plurality of scales on said dial, each of said scales having such a radius that the frequency separation thereon will be substantially the same for the several scales, means for indicating the frequency to which said receiver is tuned to respond, and means controlled by the motion of said tuning element past the positions giving the limiting reactance values of said element to simultaneously alter said last mentioned means, and the portion of the wave length band through which said receiver is adapted to tune.

9. In a radio receiver adapted to receive signals covering a broad wave length band, which includes an inductance variable in steps to permit tuning throughout various portions of said band, the combination of a variable tuning element, a dial associated with said element and movable therewith, a plurality of frequency calibrated scales on said dial, the radii of the scales for the short wave lengths being greater than the radii of those for the long wave lengths, means for indicating the frequency to which said receiver is tuned to respond, and means for designating the scale relative to which said indicating means is effective as said inductance is varied in steps.

10. In a receiver adapted to receive signals covering a broad wave length band in which an inductance is varied in steps to permit tuning through various portions of the band, a variable condenser for tuning said receiver, a plurality of scales of different length, an indicating means for cooperation with said scales, means for moving said indicating means and scales relative to each other for indicating the position of said variable condenser, and means for designating the scale relative to which said indicating means is effective as the inductance of a circuit of the receiver is altered in steps, said last mentioned means causing the longer of said scales to be effective in the short wave length portion of the band and the shorter of said scales to be effective in the long wave length portion of said band.

11. In a radio receiver adapted to receive signals covering a broad wave length band, which receiver includes an inductance variable in steps to permit tuning through the various portions of said band, the combination of a variable tuning element, a plurality of scales of different length, indicating means for cooperation with said scales, means for moving said indicating means and said scales relative to each other for indicating the frequency to which said receiver is tuned, and means controlled by the motion of said tuning element past the positions giving the limiting reactance values of said variable tuning element to simultaneously alter the portion of the wave length band through which said receiver is adapted to tune, and select the scale relative to which said indicating means is operative, said last mentioned means causing the longer of said scales to be effective in the short wave length portion of the band.

12. In a receiver adapted to receive signals covering a broad wave length band in which an inductance is varied in steps to permit tuning through various portions of the band, a variable condenser for tuning said receiver, a plurality of scales operatively related'to said condenser for indicating the frequency to which said receiver is tuned, the scales for the successive short wave portions of the band being of progressively greater length than those for the long wave portion of said band, an indicating means for indicating the position of said variable condenser, and means for designating the scale relative to which said indicating means is efiective as the inductance of a circuit of the receiver is altered in steps.

13. In a radio receiver for receiving radio signals covering a broad frequency band and employing reactance elements variable in steps to permit tuning throughout the various portions of the band, the combination with a variable reactance element for tuning throughout the various portions of the band, of a plurality of scale means, each of difierent length and each bearing indices of the frequencies covered by said variable reactance element while operating to tune within the respective portions of said band, a frequency-indicating means for cooperation with said scales, means for moving said scales and said indicator means relativeto each other as said variable reactance element is varied to tune said receiver, and means for causing the longer of said scales and the indicating means to cooperate to indicate frequencies in the high-frequency portions of said band and the shorter of said scales and the indicating means to cooperate to indicate frequencies in the low-frequency portions of said band.

14. In a radio receiver for tuning in a plurality of frequency bands a tuning element continuously variable and a tuning element variable in steps, scales associated with said continuously variable element for indicating frequency in each of said bands, each scale being longer as the frequency band to which it relates is higher, a control means for varying said continuously variable element and for moving said scales relative to an index and means for indicating the scale in use.

15. In a radio receiver for tuning over a, plurality of frequency bands, a tunable circuit including a first tuning element continuously variable over each of said bands and a second tuning element adjustable in steps corresponding to said bands, scales for indicating in each of said bands the frequency to which said variable tuning element is adjusted, each scale being longer as the frequency band to which it relates is higher, means associated with said second tuning element for selecting the scale corresponding to the band for reception in which said second tuning element is adjusted, and means controlling simultaneously the variation of said variable tuning element and the indicatiofi on said selected scale of "the frequency to which saidreceiver is tuned.

HAROLD MILLER LEWIS.

CERTIFICATE OF CORRECTION.

mm No. 1,987,857. January 15,1935.

HAROLD MILLER LEWIS.

'It is hereby certified that error appears in the printed specification of the above numbered patent requiring correction as follows: Page 4, second column, line 69, claim 6, for "wave length" read frequency; and that the said Letters Patent should be read with this correction therein that the same may conform to the record of the case in the Patent Office.

Leslie Frazer (Seal) Acting Commissioner of Patents. 

